For many years the general geometric structure of the "HONEYCOMB" cell has been known and applied in various applications and for various purposes. More particularly, honeycomb cellular core structures of corrugated fibreboard are known and find wide utility in modern industry. For example, corrugated fiber board honeycomb is used as the core material in sandwich type construction typically used to produce items such as hollow core flush doors, interior portable wall partitions, and the like.
One method of manufacturing such materials developed during the 1960's, and still in use today, involved laying up a series of flat sheets with alternate solid lines of glue, compressing and drying the stack thus formed, and then cutting the entire pile into strips to the desired thickness. When the strips were then pulled from the opposite sides of the stack, the honeycomb pattern emerged. One example of this prior art method is that disclosed in U.S. Kauffman Pat. No. 3,301,729. In the Kauffman patent the cellular core structures of corrugated fibreboard comprise a plurality of strips of the material superimposed to form a stack, with spaced areas of adjacent strips being glued or otherwise adhered together. The adhered areas between one strip and adjacent strip are spaced apart along the length of the strips, and the adhered areas between that one strip and an adjacent strip on the other side thereof are intermediate the first mentioned areas so that the stack can then be expanded to define a cellular core structure to which several face sheets may be adhered, all in well known manner.
However, the Kauffman '729 patent method has several following shortcomings:
1. The kerf of any saw blade used to cut the stack into strips of desired thickness creates substantial amounts of dust which is pure wasted material. PA1 2. The paper dust created by such sawing is hard to control and creates potential health and disposal difficulties. PA1 3. Excessive paper dust in the corrugated flutes of the finished product is objectionable to the user, creating problems in subsequent assembly operations. PA1 4. Glue lines formed by the glue stripping rolls are hard to control and often irregular in width; too wide a glue line restricts the expansion of the honeycomb cell, requiring more fiberboard to begin with, and less-even distribution of the core within the users' product. PA1 5. The method involves the separate operations of lay-up, compression and cutting, a rather labor intensive process which also requires the handling and "staging" of the product in various forms as it proceeds through the production area. PA1 1. Reduce the amount of material initially required by providing for narrower joints and pre-creased cell corners as well as eliminating the end tabs of the Kauffman Patent which were required to hold the sheet together during the die cutting process. PA1 2. Create more uniform cell sizes by use of printing small "glue" spots and creasing the cell corners. PA1 3. Eliminate paper dust and excessive waste through the die cutting process. PA1 5. Provide a process designed to handle the radically die cut intermediate product sheet which would be difficult, if not impossible, to handle without the "in-line" process and the specially designed "tie-in" equipment.
Another prior art approach to making honeycomb structure as core material for building panels, doors, table tops, etc. as an interior reinforcing core material, in a continuous process including a star folding operation, is exemplified in the varying approaches taught in the prior art U.S. Pat. No. to Payne et al 3,082,142 and Lincoln et al 2,553,054; and in the series of U.S. Pat. Nos. to Geschwender 3,218,217; 3,528,334; 3,587,479; 3,607,583; 3,684,618; and 3,887,419. However, these various prior art approaches to continuous production of honeycomb material all involved the use of flexible material (such as heavy paper) which can be and was web fed in continuous form, and such approaches cannot be employed with sheet material such as corrugated fibreboard. In those prior art approaches, which proposed employing rotary die cutting, the "state-of-the-art" in die cutting had not progressed to the point wherein a quality product could be produced from commercially available rotary die cutting equipment once the necessary "tie-in" equipment to handle the sheet had been developed.
Other prior art patents of general interest to the present invention include the following U.S. Pat. Nos.:
1,455,061 Barrett PA2 2,537,026 Brugger PA2 2,581,421 Lombard et al PA2 3,810,800 Doll
However, through the years, both die cutting equipment and techniques have improved to the point where, in accordance with the present invention, and through the combined use of standard equipment and specially designed material handling equipment, as well as improvements in die cut and glue patterns, an improved process and apparatus has been developed in accordance with the present invention for producing corrugated fibreboard honeycomb which essentially solves the aforementioned objections.